Plastic articles have replaced glass, metal, and wood articles, because plastic can be engineered to not shatter, rust, or rot. The durability of plastic articles also creates a disposal dilemma. In addition, many plastic resins are made from petrochemicals, which have long-term supply and cost issues.
Therefore, there is a considerable effort underway to find biologically-derived and sustainable sources of thermoplastic resins. These bio-derived polymers are more sustainable, because they are derived from renewable sources and can be made from domestically produced monomers. Preferably, these polymers are also biodegradable or compostable to resolve the disposal dilemma.
Polylactic acid, also known as polylactide or PLA, has been explored as a thermoplastic resin from biologically sustainable origins. The visual transparency and compostability of PLA make it an attractive material for film-based applications, such as retail and food packaging. However. PLA has a high transition glass temperature of about 60° C., which correlates to a rigid and glassy state of the polymer in an ambient temperature range. As a result. PLA does not provided the flexibility desired for most packaging applications.
Attempts to add plasticizers to increase PLA's flexibility have provided only marginal improvement, and may be even counterproductive, sometimes causing the composition to transform from an amorphous to a crystalline state, which is typically more rigid and brittle.